摘要:

The paper gives, first a brief review of the use of electricity in coal mines from 1908 to the present time, secondly a statistical summary of the position as it now stands, and finally the author's view of possible future developments.The early part of the period under review was a period of some difficulty. An average death roll from coal-dust explosions of more than 250 persons per annum over a period of 5 years, added to the fact that electricity was widely suspected of having been the originating cause of the most disastrous explosion in the history of British mining, namely that at Senghenydd Colliery, South Wales, in October, 1913, had the effect of causing the miners to call for the removal of electricity from the pits. Happily, by the application of systematic stone-dusting, a means was found of preventing the spread of an explosion of gas or coal-dust, and thereafter the miners' opposition lessened, at any rate in degree. It has not yet disappeared.During the last 10 years the coal industry has been greatly assisted by mechanized mining and mechanical methods of coal-sorting. These, with normal development in other directions, have resulted in a total of 2 162 01.5 h.p. of motors installed in 1937, made up of just over 1 000 000 h.p. above-ground and the same below-ground.Accident statistics are touched upon. It is recorded that taken over 10 years, 1927–1936 inclusive, electricity has been responsible for 224 out of 8 656 deaths, or 2½% of the total loss of life in the pits. The position in respect of the number of electrical accidents has not improved during recent years, but at the same time the number of men exposed to the risk of electrical accident has steadily increased year by year.The last section of the paper consists of a forecast of probable future developments. The author concludes with an appeal to electrical engineers to capture, if possible, the confidence of the miners.

DOI:10.1049/jiee-1.1939.0093

出版商:IEE    

年代:1939

数据来源: IET

摘要:

The paper deals with the engineering aspect of Empire telegraph communications. In order that the size and scope of these communications may be realized, the author begins by setting forth the components of the telegraph operating company, showing the systems contributed by each section.The engineering organization within the operating company is then dealt with, the training and necessary qualifications of telegraph engineers in the present service being outlined. Returning to the general aspect of Empire communications, the main traffic routes are discussed, with details of a number of main-line circuits. Some of the engineering requirements of the flow of traffic are touched on.Having dealt briefly with the system, the paper proceeds to enumerate the methods by which the collection and the delivery of messages are effected. The methods of signalling and the suitability of the different codes under varying circumstances are explained.The author then presents a short history of progress in cable telegraphy. Modern methods of signal shaping, balancing, and synchronous-regenerator working on cable circuits are reviewed. Where well-known methods are in use the descriptions are brief, full technical explanations being given only where information has not previously been published except in patent specifications. The items described in detail include the capacitance magnifier, the fork relay, the automatic bias corrector, and the automatic scrutinizer.There follow brief notes on recent progress and cable problems which are still being investigated.A brief outline of the methods of operating the wireless telegraph circuits is given, with details of the application of regenerator working to these circuits. A description of a method of double-frequency keying of wireless circuits follows. Finally, reference is made to the effects of varying cosmic conditions on wireless signals.

DOI:10.1049/jiee-1.1939.0104

出版商:IEE    

年代:1939

数据来源: IET

摘要:

The present paper gives the results of an investigation carried out by means of the restnking-voltage indicatorf (r.v.i.), on the parameters determining rates of rise of voltage for switches in a large 33-kV substation fed through 16½ miles of 66-kV cables and three 50,000-kVA 66/33-kV transformers. The measurements were made on one set of transformers, and the results are used to deduce the transients of restriking voltage under the worst service conditions and are applicable in general to transformer substations fed by a long transmission system.The highest rate of rise of voltage which appears to exist is 970 volts/microsec. (say 1 000 volts/microsec). This will only occur when the rupturing capacity on the busbars is relatively small, the fault being supplied through a single transformer. The highest rate of rise of voltage encountered when the heaviest fault currents are involved (supply through three transformers) is 625 volts/microsec. The circuit oscillation frequencies encountered are quite low (8–14 kc./sec), and it is concluded that for frequencies of this order it is quite safe to calculate transients of restriking voltage on the assumption that the main system parameters concerned (L1,C1are approximately equal to their values measured at supply frequency. There is, however, some evidence that even at these. relatively low frequencies the effective leakage inductance of the transformers is about 7% less than the effective value at power frequency: and it is accordingly suggested that, until further information becomes available, caution should be observed in using 50-c/sec. values of transformer leakage inductance to calculate rates of rise of voltage when the natural frequency of the system concerned is much above 20 kc/sec. Methods are described by means of which transients of restriking voltage may be calculated in appropriate cases.

DOI:10.1049/jiee-1.1939.0108

出版商:IEE    

年代:1939

数据来源: IET

摘要:

An account is given of the performance of the split-anode magnetron when working at frequencies such that transit time can be neglected. An, accurate and convenient method is described of determining this performance from the measurement of valve resistance at power frequencies. A series of results for one valve are included; these show the general influence of the various operating conditions.The anode modulation and frequency stability of the valve are discussed, while some measurements at radio frequency are given and the agreement of the two methods is found to be good.

DOI:10.1049/jiee-1.1939.0109

出版商:IEE    

年代:1939

数据来源: IET

摘要:

The paper describes some of the physical mechanism involved in frequency-division by valve circuits; requirements which must be satisfied for such division to occur without free self-oscillation being derived. A practical circuit for this purpose is developed from this theory, and the form in which it has actually been used described; together with the results of some experiments on stability carried out on dividers of this type. In conclusion, some more complex systems which might form subjects for future practical investigation are indicated schematically.

DOI:10.1049/jiee-1.1939.0110

出版商:IEE    

年代:1939

数据来源: IET

摘要:

A method is given for localizing cable faults which flash over at a high voltage and heal at lower voltages. A new meter, which is used in the method described, and the auxiliary apparatus, are outlined briefly. The method of calculating the position of the fault is given in detail, and a correction factor is found semi-empirically to allow for the effect of the line. The theory of the discharge phenomenon is considered, and some experiments made under controlled conditions to check the theory provide oscillograph illustrations.

DOI:10.1049/jiee-1.1939.0111

出版商:IEE    

年代:1939

数据来源: IET

摘要:

A solution due to Jacottet, of the problem of the distortion of a vertical-fronted voltage wave of infinite length as it travels along a simple line, is used as a basis for the development of formulae and curves for the attenuation and distortion of chopped waves, and of waves with vertical or finite fronts and exponential tails. These results are employed to show how to obtain limiting values for the original shape and amplitude, and distance travelled of a wave recorded at any point on a simple line, and also to calculate its behaviour at any other point.Using Bekku's method of subdivision of waves, formulae and curves are developed to calculate the attenuation and distortion of waves on single- and three-phase power transmission systems for disturbances in any or all lines, and it is shown how phenomena observed in practice may be accounted for. The effect of earth wires is also considered.The results obtained are compared with oscillograms of artificially produced surges in three-phase power transmission lines, and excellent agreement is obtained.

DOI:10.1049/jiee-1.1939.0113

出版商:IEE    

年代:1939

数据来源: IET

摘要:

A previous paper discussed the nature of fluctuation noise in thermionic valves which are either perfectly temperature-limited or perfectly space-charge-limited. It was suggested that the noise should be represented by a “shot noise” formula in the former, and a “thermal noise” formula in the latter, but, since perfection is difficult to achieve, the case of more practical value is the valve which is mainly space-charge-limited, but not entirely free from temperature limitation. A method of quantitative estimation of the noise in diodes under such conditions (in terms of the current/voltage characteristic) is the subject of this further paper.

DOI:10.1049/jiee-1.1939.0114

出版商:IEE    

年代:1939

数据来源: IET

DOI:10.1049/jiee-1.1939.0115

出版商:IEE    

年代:1939

数据来源: IET

DOI:10.1049/jiee-1.1939.0123

出版商:IEE    

年代:1939

数据来源: IET